Question

Please help! i only get decimals as the answer!..


The half-life of a certain radioactive material is 72 days. An initial amount of the material has a mass of 344 kg. Write an exponential function that models the decay of this material. Find how much radioactive material remains after 5 days. Round your answer to the nearest thousandth.

Answer 1

... represents moving along into infinity, or the deletion of steps :/

Answer 2

This is regular radioactive decay which is an exponential decay given by:
\[N(t) = N _{0}e ^{-kt}\]
Where you have some initial amount N0, a decay constant 'k', and some time exlapsed 't'

Answer 3

A=Pe^(rt) ; divide of the P

A/P = e^(rt) ; ln the sides

ln(A/P) = rt ; divide off the t to find r

ln(A/P)
------ = r ; since A = P/2
t

ln(1/2) /t = r ; and t = 72

plug this back in as "rate" in: A = P e^(rt) to determine the rest


is my thought

Answer 4

i spose Amount and Principle dont apply in biology; but ... you know :)

Answer 5

That's correct, only that since it's a decay, not a growth, the exponent is negative.

Answer 6

ln(1/2) = -ln(2)

Answer 7

@Lunarwolf58
It's really useful to remember that if T is the half-life (or the doubling time, for a growth equation), then kT = ln(2)